Hot mix asphalt (HMA) is a material used extensively in paving roads, runways, parking areas, etc. HMA is a mixture of liquid asphalt, aggregate, and special additives. The special additives modify the final product to yield a particular set of properties suitable both to the finished material, and to handling during manufacturing, transportation, and laying of the surface. HMA is manufactured by bringing together various ingredients at an elevated temperature, mixing the ingredients, and storing the finished product before transporting to the use site.
HMA as the name implies, is hot, with typical temperatures up to and exceeding 340° F., causing problems with cleaning operations. The liquid asphalt is liquid at the elevated temperatures where it is processed into HMA, but the mixture becomes sticky and eventually solid as the temperature falls. During the manufacturing and handling processes, HMA adheres to nearly every surface it contacts. Thus, during the paving process, HMA adheres to the equipment involved in manufacturing the asphalt, in transporting the asphalt to the paving site, and in disposing the asphalt onto the particular site. The build-up of HMA on contact surfaces can result in inefficient or faulty operation of the equipment. Furthermore, at temperatures exceeding 340° F., combustible components of the HMA and liquid asphalt may catch fire, especially when built-up materials adhere to the hot mixing surfaces of the drum or pug mill.
To prevent the asphalt from sticking or adhering to the bed of the transportation vehicle, an asphalt release agent is applied to the bed prior to loading the asphalt. Various other methods are used to clean the components of the asphalt plant. Diesel fuel or similar solvents can be used to clean some components, but the risk of fire and explosions, as well as environmental concerns, render this method undesirable. Adhered asphalt can be removed using mechanical force, such as air hammers and chisels. However, this process is time consuming, ineffective, is dangerous to personnel, and can result in damage to the machinery.
Cold mix asphalt (CMA) is similar to HMA, but is mixed at a lower temperature. Also, some ingredients may be different. Despite the differences, cleaning CMA from the manufacturing plant or equipment involves many of the same problems mentioned above.
Thus, there is a need in the industry for a method of cleaning asphalt contact surfaces that overcomes at least these disadvantages.